In the case of bearing journals, in particular bearing journals of Cardan spiders (joint spiders) of Cardan joints, there is the general problem that it is sought to obtain as long as possible a bearing length in relation to the structural size using as simple as possible a production method. At the same time, the bearing journal should have as cylindrical a form as possible at least in the region of the bearing length, that is to say the lateral surface should, at least in the region of a bearing section, correspond as accurately as possible to a cylinder barrel, in particular to a shell of a circular cylinder, so as to form a good running surface for rolling bodies, in particular needle rollers.
Cardan spiders (joint spiders) with bearing journals, wherein the longitudinal central axes of the bearing journals lie in a plane and the longitudinal central axes of successive bearing journals are each at right angles to one another, or tripods in which three bearing journals lie in a plane, the longitudinal central axes of which journals each enclose an angle of 120° with one another, are conventionally produced by extrusion, in particular transverse extrusion. The production of a Cardan spider by extrusion, in particular transverse extrusion, emerges for example from DE 2819167 A1. The two dies (mould halves) have aligned cylindrical channels running at right angles to the parting plane between the dies, into which channels there is inserted a blank. Press punches are moved through the cylindrical channels toward the cylindrical blank from both sides, whereby a flow of the material of the blank into cutouts of the dies is effected, which cutouts adjoin the cylindrical channels in the region of the parting plane and have the shape of the journals to be formed. The material flow that forms the journals thus takes place transversely with respect to the direction in which the press punches are moved.
The face surface at the free end of the respective bearing journal is formed by a freeform surface. This forms an elevation of the face side of the bearing journal, said elevation being convex in the direction of the end of the journal. The transition between said freeform surface and the substantially cylindrical lateral surface of the bearing journal forms the end of the bearing section of the lateral surface and thus delimits the bearing length of the bearing journal.
To improve the cylindricity of the bearing journal in the region of the bearing section of the lateral surface, reworking of the bearing journal is normally performed. For this purpose, a grinding operation may for example be performed. Grinding operations however have the disadvantage that they are time-consuming and expensive, and therefore grinding operations of said type should be avoided as far as possible. From EP 0891825 B1, it is known, in the case of bearing journals, in this case in particular tripods, to perform a rolling operation for reworking after the extrusion process. During said rolling operation, it is possible, if desired, for grooves that run in encircling fashion around the bearing journal to simultaneously be formed into the lateral surface of the bearing journal.